Paget's is a disorder of bone remodeling. The process is initiated by an increase in osteoclast mediated bone resorption followed by an abundance of new but abnormal bone formation. This study will determine the number of osteoclast precursors, the level of IL-6 and the presence or absence of measles virus nucleocapsid mRNA in the peripheral blood from patients with Paget's disease at the start of their scheduled treatment with the antiresorptive bisphosphonate alendronate and at the completion of the 6 month treatment. The number of osteoclast precursors and the IL-6 levels will be correlated with the activity of the disease as determined by the levels of serum and urine markers of bone resorption and formation.